Steering columns in automobiles are generally equipped with angular contact bearing assemblies comprising a conductive inner ring with a concave recess forming a first raceway, a conductive outer ring with a concave recess forming a second raceway and a set of conductive balls contacting both the first raceway and the second raceway. In order to simplify the mounting of the inner ring on a central shaft of the steering column, the inner ring is mounted on the shaft via a sleeve or tolerance ring, which is usually moulded of non-conductive plastics in order to allow for some flexibility and to reduce the costs.
Steering wheels mounted on the shaft often contain electrical switches or devices and/or airbags, which may be affected by electrostatic charges accumulating on the steering wheel.
It is therefore important to ensure an electrical grounding of the steering wheel by ensuring a conductive contact between the shaft of the steering column and the chassis of the automobile via the angular ball bearings. As a matter of course, this conductive contact could be used for transmitting electrical signals as well.
The document U.S. Pat. No. 4,530,609 teaches to make the sleeve conductive by using a graphite-filled polymer material, which is, however, fairly expensive.
In order to ensure the electrical contact, mentioned above the document FR 2782758 A1 teaches to use a conductive part creating an electrically conductive contact between the inner ring and the shaft. This conductive part is a generally ring-shaped member arranged between an axial end face of the sleeve and a wavy spring or ondular washer generating an axial preload of the angular bearing. The wavy spring is preloaded with a fixing ring fitted over the shaft.
The ring-shaped member is provided with a ring-shaped main body and a latch bent around the profile of the sleeve so as to overlap with a surface supporting the inner ring such that the inner ring is in contact with the latch. The electrically conductive contact between the outer ring and the shaft is therefore established from the outer ring via the balls, the inner ring, the latch, the main body of the ring-shaped member, the wavy spring, and the fixing ring.
A similar solution with a conductive element having a ring-shaped main body and multiple latch-like axial protrusions engaging in slots of the sleeve is proposed in the document U.S. Pat. No. 6,675,360 B1.
A solution where the latches are immediately formed on the wavy spring is proposed in US 2010/0308569A1. A solution where latches are formed on the inner ring is proposed in DE 102 20 688 B4.
In this conductive pathway, there is a high number of contact points which are susceptible to degradation or interruption of the contact and the total probability of failure accumulates the individual probabilities. The conductive parts risk to break or be shifted from their proper position. This may lead to problems during the assembly or interruptions of the contact. The loose parts may damage other parts of the steering column or its surroundings.